Bi-directional tapered roller bearing assembly with improved wear resistance

ABSTRACT

The wear resistance of a bi-directional tapered roller bearing is improved by applying a tribological coating to both the small and large end faces of the roller and to at least one of the rib faces of the bearing assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/US2008/053947, filed Feb. 14, 2008, which claims priority to U.S.Provisional App. No. 60/892,061, which was filed on Feb. 28, 2007. Thedisclosures of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present disclosure relates to tapered roller bearings, and inparticular, to a bi-directional tapered roller bearing having improvedwear resistance.

BACKGROUND ART

Examples of bi-directional tapered roller bearings are shown in U.S.Pat. Nos. 6,464,401 and 5,735,612, which are incorporated herein byreference. Bi-directional bearings handle axial loads in both axialdirections. Such bearings include a cone defining a tapered innerraceway, a cup defining a tapered outer raceway and a plurality oftapered rollers between the inner and outer raceways. The bearingassembly includes at least a thrust rib on the cup adjacent the largediameter end of the roller and a second rib on the cone adjacent thesmall diameter end of the roller. The two ribs have associated ribfaces, and the rollers are positioned between the two rib faces. Incontrast, a uni-directional tapered roller bearing will have only asingle thrust rib.

Bi-directional tapered roller assemblies are susceptible to abrasive andadhesive wear at the sliding contacts between the rolling elements andthe cup/cone rib faces in the presence of debris or in low lubrication(e.g., oil-out) conditions. Experiments have shown that both internallygenerated and external debris are especially harmful at the rib-rollerend contacts because they can become trapped within the multi-ribbearing and cannot easily flow away from the rib/roller end contacts.Similarly, the presence of extra rib-roller end sliding contactsrelative to single rib tapered roller bearing designs can makebi-directional tapered roller bearings more susceptible to rib-rollerend scuffing or scoring damage in oil-out condition.

BRIEF SUMMARY

A bi-directional tapered roller bearing comprises a tapered innerraceway, a tapered outer raceway facing the tapered inner raceway, and aplurality of tapered rollers positioned between the tapered inner andouter raceways. The tapered rollers have a side surface, a large endface at a large diameter end of the tapered roller and a small end faceat a small diameter end of the tapered roller. The bearing includes atleast a first rib at one of an axial inner or outer edge of the innerraceway and a second rib at the other of the axial inner and outer edgesof the outer raceway. The first and second ribs each define a rib face.One of the rib faces is adjacent the large end of the tapered roller andthe other rib is adjacent the small end of the tapered roller. We havefound that by applying a tribological coating to both the large end andthe small end of the tapered roller the wear resistance of the bearingcan be improved. The coating can also be applied to at least one of thefirst and second rib faces.

The coating can have a thickness of less than 10 μm and a hardness equalto or greater than the hardness of the substrate to which it is applied.The coating can, for example, have a hardness of at least about 9 GPa asmeasured by nanoindentation with a Berkovich diamond indenter.

The coating comprises an amorphous carbon-based or hydrocarbon-basedthin film coating. The coating can be reinforced with titanium (Ti),tungsten (W), chromium (Cr), tantalum (Ta), silicon (Si), vanadium (V),nickel (Ni), niobium (Nb), iron (Fe) or zirconium (Zr) or carbidicinclusions thereof. In a specific embodiment, the coating can comprise atungsten carbide-reinforced amorphous hydrocarbon nano-compositecoating.

The coating comprises an adhesion layer applied to the surface of thesubstrate to be coated and a top functional layer over the adhesionlayer. The adhesion layer can be chromium (Cr), titanium (Ti), tantalum(Ta), nickel (Ni), molybdenum (Mo), iron (Fe) or silicon (Si). Althoughit is preferred that the adhesion layer be comprised of the dominantelement only (e.g., 100 atomic % Cr), it can include other elements suchas carbon (C), hydrogen (H), oxygen (O) and combinations thereof.However, if the adhesion layer includes C, H or O, the C, H and/or Oshall comprise no more than about 75 atomic % of the adhesion layer.That is, the dominant element comprises at least 25 atomic % of theadhesion layer.

The top functional layer can be a hard carbonaceous layer that iscomprised of amorphous carbon or amorphous hydrocarbon. The topfunctional layer can consist only of amorphous carbon (C) or amorphoushydrocarbon (a:C—H). Alternatively, the top functional layer can includethe elements oxygen (O), nitrogen (N), boron (B), fluorine (F) orcombinations thereof. The carbonaceous top layer may also include Ti, W,Cr, Ta, Si, V, Nb, Zr, Mo, O, N, B, F or combinations thereof asadditive elements. However, the additive element(s) shall not exceed 50atomic % of the total top layer composition, the balance of compositionbeing carbon and hydrogen. It is also possible for the carbonaceousfunctional top layer to have no additives and consist of only amorphouscarbon or amorphous hydrocarbon.

In one variation, the coating can include a gradient layer between theadhesion layer and the top functional layer. In this instance, thegradient layer transforms from the composition of the adhesion layeradjacent the adhesion layer to the composition of the top functionallayer adjacent the top functional layer. In another variation, thecoating can include a Cr/WC/a-C:H gradient layer over the adhesion layerand a WC/a-C:H mid-layer over the gradient layer. The top functionallayer covers the mid-layer and is comprised of a-C:H.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a bi-directional tapered rollerbearing applied to a member;

FIG. 2 is an enlarged fragmentary cross-sectional view of the bearing;and

FIG. 3 is an enlarged schematic drawing of a coating applied to asurface of the bearing.

Corresponding reference numerals will be used throughout the severalfigures of the drawings.

DETAILED DESCRIPTION

The following detailed description illustrates the invention by way ofexample and not by way of limitation. This description will clearlyenable one skilled in the art to make and use the invention, anddescribes several embodiments, adaptations, variations, alternatives anduses of the invention, including what we presently believe is the bestmode of carrying out the invention. Additionally, it is to be understoodthat the invention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or being carried outin various ways. Also, it is to be understood that the phraseology andterminology used herein is for the purpose of description and should notbe regarded as limiting.

A bi-directional tapered roller bearing 10 is shown generally in FIGS. 1and 2. The bearing 10 comprises a cone 12 defining an inner taperedraceway 14, a cup 16 defining a tapered outer raceway 18, and aplurality of tapered rollers 20 positioned between the inner and outerraceways. The rollers are separated from each other by a cage 22. Therollers 20 each have a large diameter end 20 a, a small diameter end 20b and a tapered surface 20 c. The inner and outer raceways 14 and 18 andthe roller surface 20 c are all formed such that there is rolling motionbetween the rollers and the raceways. The cone 12 includes a thrust rib24 at a wide diameter end of the raceway 14. A rib ring adjacent thesmall diameter end of the raceway 14 defines a retaining rib 26 which isadjacent the small diameter end of the raceway 14. A third rib 28adjacent the cup 16 is positioned to be adjacent the large diameter end22 a of the roller. The retaining rib 26 is separate from the cone 12and the third rib is separate from the cup 16 to facilitate assembly ofthe bearing assembly. The ribs 24, 26 and 28 each define respective ribfaces 24 a, 26 a and 28 a, respectively which are generallyperpendicular to the raceway. The rib 24 is shown to be integral withthe cone 12, while the ribs 26 and 28 are shown to be separate fromtheir respective races. However, the bearing assembly can be made withthe ribs 26 and 28 integral with their races and with the rib 24 beingseparate from its race.

Sliding contact occurs between the large and small ends of the rollersand the rib faces. Hence, in the bearing 10, sliding contact will occurbetween the roller large end 20 a and the rib faces 24 a and 28 a aswell as between the roller small end 20 b and the rib face 26 a.Experiments have shown that both internally-generated and externaldebris are especially harmful at the rib-roller end contact because thedebris can become trapped within the multi-rib bearing assembly, andcannot easily flow away from the rib/roller interface. Further, thepresence of the extra rib/roller interfaces (as compared touni-directional thrust tapered roller bearings which have only a singlethrust rib) makes bi-directional roller bearings more susceptible torib-roller end scuffing or scoring damage in oil-out conditions.

If a bi-directional tapered roller bearing experiences failure, thedebris generated from the raceways cannot escape the contact regions.This leads to severe adhesive wear at the sliding rib-roller endcontacts, ultimately resulting in excessive bearing torque (andfailure). Application testing with coatings on only the roller ends 20a,b protected the roller end surfaces, but did not prevent massiveadhesive wear damage on the rib faces that resulted from debrisparticle/rib face adhesive interactions in the sliding contacts. Coatingat least one rib face in addition to the roller ends is expected todelay debris-related failure of the rib and thus improve the overallwear resistance of the bearing.

The coating is an amorphous carbon or hydrocarbon (sometimes referred toas a diamond-like carbon, or DLC) based thin film tribological coating.As just noted, the coating is applied to the roller end faces andoptionally to one or both of the rib faces. Preferably, the coating isapplied to the end faces of all the rollers in the bearing assembly. Oneacceptable coating is a WC/aC:H coating available from The TimkenCompany under the name ES300. The coating has a thickness of less thanabout 10 micrometers. The coating has a hardness equal to or greaterthan the hardness of the substrate to which it is applied. The coatingcan, for example, have a hardness of at least about 9 GPa as measured bynanoindentation with a Berkovich diamond indenter. The DLC coating canbe reinforced with additional elements such as titanium (Ti), tungsten(W), chromium (Cr), tantalum (Ta), silicon (Si), vanadium (V), nickel(Ni), niobium (Nb), iron (Fe) or zirconium (Zr) or carbidic inclusionsthereof. In one illustrative embodiment, the coating is a tungstencarbide-reinforced amorphous hydrocarbon nano-composite coating. Thetungsten carbide-reinforced amorphous hydrocarbon nano-composite coatingis a member of this class.

The coating C (FIG. 3) comprises at least two layers, an adhesive layeror interlayer 40 which is applied to the substrate S (i.e., rib face orroller end) and a top functional layer 42 which covers the adhesionlayer 40. The adhesion layer can be chromium (Cr), titanium (Ti),tantalum (Ta), nickel (Ni), molybdenum (Mo), iron (Fe) or silicon (Si).Although it is preferred that the adhesion layer 40 be comprised of thedominant element only (e.g., 100 atomic % Cr), it can include otherelements such as carbon (C), hydrogen (H), oxygen (O) and combinationsthereof. However, the C, H and/or O shall comprise no more than about 75atomic % of the adhesion layer. Stated differently, the dominant elementcomprises at least 25 atomic % of the adhesion layer.

The top functional layer 42 comprises amorphous carbon (or amorphoushydrocarbon). The top functional layer may include the elements oxygen(O), nitrogen (N), boron (B), fluorine (F) or combinations thereof. Thecarbonaceous top layer may include one or more of the additive elementsnoted above (Ti, W, Cr, Ta, Si, V, Nb, Zr, Mo, O, N, B, and F). However,the amount of additive element(s) shall not exceed 50 atomic % of thetotal top layer composition, the balance of the top layer compositionbeing carbon and hydrogen. It is also possible for the carbonaceousfunctional top layer to have no additives and consist of only amorphouscarbon (C) or amorphous hydrocarbon (C and H).

Typically, for a steel substrate, the adhesion layer 40 will be chromium(Cr) and the functional layer 42 will be a hard carbonaceous layer. Agradient layer 44 can be formed between the adhesion layer 40 and thetop functional layer 42 with the gradient layer transforming from thecomposition of the adhesion layer to the composition of the final or topfunctional layer. Coatings with additional layers are also included,such as Cr (adhesion layer)+Cr/WC/a-C:H (gradient layer)+WC/a-C:H(mid-layer)+a-C:H (top layer). In this instance, the gradient layer willtransform from being chromium adjacent the adhesive layer to beingWC/a-C:H. The WC/a-C:H mid-layer will then transform from being WC/a-C:Hadjacent the gradient layer to being a-C:H adjacent the top functionallayer. Hence, the mid-layer defines a second gradient layer. It isimportant that the top functional layer be a hard carbonaceous layer inany embodiment of the coating (which may or may not include the otherelements as described above).

The coating composition that is applied to the roller end faces and therib faces need not be the same. For example, the a WC/a-C:H coating canbe applied to the roller ends and a TiC/a-C:H coating can be applied tothe rib faces.

The coating can be deposited using plasma techniques for vapordeposition, but is not limited to physical vapor deposition (PVD) orplasma-enhanced chemical vapor deposition (PECVD). As is known, thegradient layers are formed by changing the ratio of components that arebeing coated onto the substrate. Thus, there is no sharp line separationbetween adjacent layers.

We expect that by applying a wear resistant coating to both the smalland large ends of all the rollers and optionally to at least one ribface will improve the wear resistance of the bearing assembly.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

1. A method of improving the wear resistance of bi-directional taperedroller bearings; the roller bearings comprising a tapered inner raceway,a tapered outer raceway facing the tapered inner raceway, and aplurality of tapered rollers positioned between the tapered inner andouter raceways; the tapered rollers having a side surface, a large endface at a large diameter end of the tapered roller and a small end faceat a small diameter end of the tapered roller; the bearing including atleast a first rib at one of an axial inner and outer edge of said innerraceway and a second rib at the other of the axial inner and outer edgesof said outer raceway, said first and second ribs each defining a ribface; one of said rib faces being adjacent the large end of said taperedroller and the other of said rib faces being adjacent the small end ofthe tapered roller; the method comprising applying a tribologicalcoating to both the large end and the small end of the tapered rollerand to at least one of the first and second rib faces; the coating beingan amorphous carbon-based or hydrocarbon-based thin film coating.
 2. Themethod of claim 1 comprising applying the tribological coating to bothsaid first rib face and said second rib face.
 3. The method of claim 1wherein said coating has a thickness of less than 10 μm.
 4. The methodof claim 1 wherein said coating has a hardness equal to or greater thanthe hardness of the substrate to which it is applied.
 5. The method ofclaim 4 wherein the coating has a hardness of at least about 9 GPa asmeasured by nanoindentation with a Berkovich diamond indenter.
 6. Themethod of claim 1 wherein the step of applying the coating comprisingapplying an adhesion layer to the surface to be coated and applying atop functional layer about the adhesion layer; the top functional layerbeing a hard carbonaceous layer.
 7. The method of claim 6 wherein theadhesion layer is chosen from the group consisting of chromium (Cr),titanium (Ti), tantalum (Ta), nickel (Ni), molybdenum (Mo), iron (Fe) orsilicon (Si); the adhesion layer being as pure as possible in thedominant element.
 8. The method of claim 7 wherein the adhesion layerincludes low levels carbon (C), hydrogen (H), oxygen (O) andcombinations thereof, the adhesion layer including no more than about 75atomic % of C, H and/or O.
 9. The method of claim 6 wherein one or moreadditives are present in the top functional layer; the additives beingchosen from the group consisting of chromium (Cr), titanium (Ti),tantalum (Ta), nickel (Ni), molybdenum (Mo), iron (Fe), silicon (Si),tungsten (W), vanadium (V), niobium (Nb), zirconium (Zr), carbidicinclusions and combinations thereof; the additives comprising 50 atomic% or less of the total top layer composition, the balance of top layercomposition being carbon and hydrogen.
 10. The method of claim 6 whereinthe top functional layer includes oxygen (O), nitrogen (N), boron (B),and/or fluoride (F)
 11. The method of claim 9 wherein the carbonaceousfunctional top layer has no additives and consists of only amorphouscarbon (C) or hydrocarbon (C and H).
 12. The method of claim 6comprising forming a gradient layer between the adhesion layer and thetop functional layer, the gradient layer transforming from thecomposition of the adhesion layer to the composition of the topfunctional layer.
 13. The method of claim 6 wherein the adhesion layeris chromium; the method comprising forming a Cr/WC/a-C:H gradient layerover the adhesion layer and a WC/a-C:H mid-layer over the gradientlayer; the top functional layer being formed over the mid-layer andcomprising a-C:H.
 14. The method of claim 1 including applying a coatingof one composition to the roller end faces and a coating of a differentcomposition to the at least one rib face.
 15. The method of claim 14wherein the coating applied to the roller end faces is a WC/a-C:Hcoating and the coating applied to the at least one rib face is aTiC/a-C:H coating.
 16. A bi-directional tapered roller bearingcomprising a tapered inner raceway, a tapered outer raceway facing thetapered inner raceway, and a plurality of tapered rollers positionedbetween the tapered inner and outer raceways; the tapered rollers havinga side surface, a large end face at a large diameter end of the taperedroller and a small end face at a small diameter end of the taperedroller; the bearing including a first rib at one of an axial inner orouter edge of said inner raceway and a second rib at the other of theaxial inner and outer edges of said outer raceway, said first and secondribs each defining a rib face; one of said rib faces being adjacent thelarge end of said tapered roller and the other rib being adjacent thesmall end of the tapered roller; the bearing further including atribological coating applied to both the large end and the small end ofthe tapered roller and to at least one of the first and second ribfaces; the coating being an amorphous carbon-based or hydrocarbon-basedthin film coating.
 17. The bearing of claim 16 wherein the tribologicalcoating is on both said first rib face and said second rib face.
 18. Thebearing of claim 16 wherein said coating has a thickness of less than 10μm.
 19. The method of claim 16 wherein said coating has a hardness equalto or greater than the hardness of the substrate to which it is applied.20. The method of claim 19 wherein the coating has a hardness of atleast about 9 GPa as measured by nanoindentation with a Berkovichdiamond indenter.
 21. The bearing of claim 16 wherein the coatingcomprises an adhesion layer applied to the surface to be coated and atop functional layer about the adhesion layer; the functional layerbeing a hard carbonaceous layer.
 22. The bearing of claim 21 wherein theadhesion layer is chosen from the group consisting of chromium (Cr),titanium (Ti), tantalum (Ta), nickel (Ni), molybdenum (Mo), iron (Fe) orsilicon (Si); the adhesion layer as pure as possible in the dominantelement.
 23. The bearing of claim 21 wherein the adhesion layer includeslow levels carbon (C), hydrogen (H), oxygen (O) and combinationsthereof, the amount of C, H and/or O in the adhesion layer not exceedingabout 75 atomic % of the adhesion layer.
 24. The bearing of claim 21wherein one or more additives are present in the carbonaceous top layer;the additives being chosen from the group consisting of chromium (Cr),titanium (Ti), tantalum (Ta), nickel (Ni), molybdenum (Mo), iron (Fe),silicon (Si), tungsten (W), vanadium (V), niobium (Nb), zirconium (Zr),oxygen (O), nitrogen (N), boron (B), fluoride (F), carbidic inclusionsand combinations thereof; the additives comprising 50 atomic % or lessof the total top layer composition, the balance of top layer compositionbeing carbon and hydrogen.
 25. The bearing of claim 21 wherein thecarbonaceous functional top layer has no additives and consists of onlyamorphous carbon (C) or hydrocarbon (C and H).
 26. The bearing of claim21 wherein the coating includes a gradient layer between the adhesionlayer and the top functional layer, the gradient layer transforming fromthe composition of the adhesion layer to the composition of the finallayer.
 27. The bearing of claim 21 wherein the adhesion layer ischromium; the coating further comprising a Cr/WC/a-C:H gradient layerover the adhesion layer and a WC/a-C:H mid-layer over the gradientlayer; the top function layer covering the mid-layer and comprisinga-C:H.
 28. A bi-directional tapered roller bearing comprising a taperedinner raceway, a tapered outer raceway facing the tapered inner raceway,and a plurality of tapered rollers positioned between the tapered innerand outer raceways; the tapered rollers having a side surface, a largeend face at a large diameter end of the tapered roller and a small endface at a small diameter end of the tapered roller; the bearingincluding a first rib at one of an axial inner or outer edge of saidinner raceway and a second rib at the other of the axial inner and outeredges of said outer raceway, said first and second ribs each defining arib face; one of said rib faces being adjacent the large end of saidtapered roller and the other rib being adjacent the small end of thetapered roller; the bearing further including a tribological coatingapplied to both the large end and the small end of the tapered rollerand to at least one of the first and second rib faces; the coating beingan amorphous carbon-based or hydrocarbon-based thin film coating; saidcoating having a thickness of less than 10 μm and a hardness equal to orgreater than the hardness of the substrate to which it is applied; thecoating comprising: an adhesion layer; the adhesion layer being chosenfrom the group consisting of chromium (Cr), titanium (Ti), tantalum(Ta), nickel (Ni), molybdenum (Mo), iron (Fe) or silicon (Si); theadhesion layer as pure as possible in the dominant element; the adhesionlayer including 0 to about 75 atomic % carbon (C), hydrogen (H), oxygen(O) and combinations thereof; and a top functional layer; the topfunctional layer including 0 to about 50 atomic % additive elements, thebalance being carbon and hydrogen; the additives being chosen from thegroup consisting of Ti, W, Cr, Ta, Si, V, Nb, Zr, Mo, O, N, B, and F.29. The bearing of claim 28 wherein the coating applied to the rollerend faces has a different composition that than the coating applied tothe at least one rib face.
 30. The bearing of claim 28 wherein thecoating applied to the roller end faces is a WC/a-C:H coating and thecoating applied to the at least one rib face is a TiC/a-C:H coating. 31.A method of improving the wear resistance of bi-directional taperedroller bearings; the roller bearings comprising a tapered inner raceway,a tapered outer raceway facing the tapered inner raceway, and aplurality of tapered rollers positioned between the tapered inner andouter raceways; the tapered rollers having a side surface, a large endface at a large diameter end of the tapered roller and a small end faceat a small diameter end of the tapered roller; the bearing including atleast first rib at one of an axial inner and outer edge of said innerraceway and a second rib at the other of the axial inner and outer edgesof said outer raceway, said first and second ribs each defining a ribface; one of said rib faces being adjacent the large end of said taperedroller and the other rib being adjacent the small end of the taperedroller; the method consisting of applying a tribological coating to thelarge end and the small end of the tapered roller and to the first andsecond rib faces; the coating being an amorphous carbon-based orhydrocarbon-based thin film coating.